1. Field of the Invention
This invention pertains to the field of cockpit indicators or display units that provide terrain information to pilot or flight crew of an aircraft.
2. Description of the Related Art
Modern avionics systems employ Head-Up Display (“HUD”) and Head-Down Display (“HDD”) systems for providing tactical flight information to the pilot. In a HUD system, a HUD unit is mounted in front of the pilot at windshield level and is directly in the pilot's field of vision. The HUD system is advantageous because the display is transparent allowing the pilot to keep his or her eyes “outside of the cockpit” while the display unit provides tactical flight information to the pilot. In a HDD system, a tactical flight display is mounted in the cockpit instrument panel directly in front of the pilot and below windshield level. To view the presentation of information on a display unit of a HDD system, a pilot must look down into the cockpit, causing him or her to take his or her eyes from the outside scene in front of the aircraft.
Modern avionics systems employ Synthetic Vision Systems (“SVS”) and Enhanced Vision Systems (“EVS”) for displaying terrain information to both HUD and HDD systems. The SVS and EVS systems are advantageous because they present terrain information of the scene in front of the aircraft to the pilot. While this is advantageous to the pilot, there are times when the presentation of terrain information could obstruct the pilot's view of the actual scene in front of the aircraft. For instance, a pilot may be flying in meteorological conditions of low visibility in which his vision of the actual terrain is obscured. In SVS and EVS systems, terrain information is provided to the pilot through HUD and HDD systems. If the aircraft flies out of the meteorological condition, typical HUD and HDD systems continue to display the terrain information. In a HUD system, the display of terrain information could obstruct the pilot's view and not allow the pilot to view the actual terrain in front of the aircraft. HUD systems may allow the pilot to lower the opacity or disable the image or provide a feature which automatically lowers the level. However, these systems do not provide a feature which will partially display the terrain image in instances where there is only a partial break out of the meteorological condition. Such instances commonly occur when the aircraft is on final approach where the terrain may be partially—but not wholly—obscured by meteorological conditions. The embodiments disclosed herein provide for automatic display of partial terrain information on an aircraft display unit thereby removing an obstruction to the pilot's view of the scene outside the front of the aircraft.
In aircraft that employs a tactical flight display using SVS and EVS systems, terrain information enhanced by an EVS may be displayed or synthetic terrain information may be displayed by an the SVS but not both simultaneously. In instances where the content information provided by the EVS does not exist or only partially exists, the pilot must switch to the SVS to receive terrain information. The embodiments disclosed herein provide for the simultaneous display of partial synthetic terrain information from an SVS and of partial enhanced terrain information from an EVS without an overlap of displayed terrain information.